Lubricating compositions comprising oil of lubricating viscosity and combinations of zinc dithiophosphates and ashless dispersants are known. It has been commonly accepted in the lubricating oil art that high levels of phosphorus, often about 0.1% by weight phosphorus in the finished lubricating oil, are necessary to provide adequate antiwear or antioxidant performance. When phosphorus content is reduced, it has been necessary to provide other additives to compensate for the loss of protection normally provided by phosphorus. Recently, environmental and toxicological problems associated with the use of organo phosphorus compounds have become a matter of serious concern. The presence of high levels of phosphorus in engine oils used to lubricate internal combustion engines has been suspected of contributing to inactivation of catalytic converters used to control emissions from gasoline engines. Additionally, high levels of phosphorus frequently interfere with performance in certain applications. For example, it has been observed that a high level of zinc dithiophosphate adversely affects transmission cooler solder corrosion. Furthermore, efficient utilization of resources is desirable, both to conserve resources and to reduce costs. It is of interest, then, that lubricating compositions be developed which employ additives containing reduced levels of increasingly scarce and costly raw materials, and materials which are suspected of contributing to environmental and toxicological problems. It is, of course, necessary that such lubricating compositions provide acceptable performance, particularly with respect to dispersancy, antioxidancy and antiwear.
U.S. Pat. No. 3,390,082 (Le Suer, et al) relates to lubricants containing an oil-soluble acylated amine wherein the acyl group is illustrated by a relatively high molecular weight substituted succinic group having at least about 50 carbon atoms in the substituent, and a phosphorus-containing substance such as a metal phosphorodithioate or adduct thereof with an epoxide.
U.S. Pat. No. 3,254,025 (Le Suer) relates to oil-soluble nitrogen and boron-containing compositions, combinations thereof with group II metal phosphorodithioates and lubricants for internal combustion engines, gears and power transmitting units.
U.S. Pat. No. 4,308,154 (Clason, et al) relates to mixed metal salts of dialkylphosphorodithioic acids and carboxylic acids, which are useful in lubricants and functional fluids as antioxidants and extreme pressure agents having improved thermal stability.
U.S. Pat. No. 4,582,618 (Davis) describes lubricating oil compositions containing less than about 0.1% by weight of phosphorus. These lubricating compositions comprise a major amount of an oil of lubricating viscosity and a minor amount of at least one oil-soluble sulfur-containing material which comprises the reaction product of sulfur and a Diels-Alder adduct in a molar ratio less than 1.7:1 wherein the adduct is an adduct of a dieneophile with at least aliphatic conjugated diene.